Year
1989
Abstract
Counting neutrons emitted by spontaneously fissioning plutonium isotopes is a means for determining plutonium content in samples.Correlation techniques have been developed for separating such neutrons from a background of nonfission neutrons due to (alpha, n) reactions. Further procedures are then used to correct the effect of neutron-induced fission. In order to perform such a correction the sample chemical composition (including the presence of moisture) must be a well known parameter. The present paper describes a new approach (add-a-source technique), proposed by H.Menlove, which could allow to correct the measurement independently by the knowledge of the sample chemical composition.\"Add-a-source\" technique is based on the measurement of the perturbation on total and coincidence rate, induced by a Californium source closely coupled to the Pu sample in assay. Such an induced perturbation is a function of the sample multiplication factor and of the probability for Cf neutrons of interacting with the sample itself.Two possible approaches, to estimate the multiplication (M) in the sample by this technique, are discussed.In the first approach, the relationship between the perturbation on total and coincidence rate and M is expressed by a system of two equations in order to avoid the need of any further calibration.As far as the second approach is concerned, the relationship between perturbation on total rat: and M must be determined through measurements on well characterized samples.